Prior art power module devices utilizing plural transistor dies are known. FIGS. 1 and 2 illustrate two such prior art configurations, FIG. 1 illustrating a device known as the SGS Thompson TH430 and FIG. 2 illustrating a device known as the Toshiba TPM1919.
The SGS Thompson TH430 shown in FIG. 1 is a four-die bipolar device incorporating a center base feed with the emitters on the outside of the rectangular array. There is no provision in this design for equalizing the path length from the base terminal to the individual die bases. It is believed that the upper frequency of the die, referred to herein as the cutoff frequency of the transistors, is close to the 50 MHz upper frequency limit of the four-die device.
The Toshiba TPM1919 shown in FIG. 2 is a 2 GHz device having four MESFET dies in a linear array. It uses an “echelon” divider structure to divide the gate signal four ways. There are matching networks between the gate connections and the ends of the divider structure. It is believed that these matching networks provide impedance transformation at the intended frequency of operation which facilitates implementation of the device. The device's input structure provides certain balancing and isolation functions. Its frequency of operation is believed to be near the upper limit of the individual dies.
Accordingly, the known prior art devices operate at the top end of the dies' frequency capability. The prior art gate and/or base wires are necessarily short because of the very high frequencies involved. As a result, their parasitic resonant (and potential oscillation) frequency is higher than the frequency at which the dies run out of gain. Thus, there is little or no oscillation.
The Motorola design MRF 154 (FIG. 2′) is described in U.S. Pat. No. 4,639,760 uses series gate resistors to intentionally substantially reduce the gain of the individual gate cells to substantially prevent oscillation. The die has gain response to >500 MHz, but the intended frequency range of the total device was <100 MHz. Thus, the Motorola design has excess gain.